It is frequently necessary to interconnect a pair of conduits or manifolds which are at least limitedly relatively displaceable. Such interconnection is frequently necessary in steam-heat systems where considerable thermal expansion and contraction frequently causes a significant shifting of conduits relative to each other. It is known to interconnect such conduits by means of an assembly formed of an inner and two outer swivel fittings in combination with two inner and two outer pipes. Each outer pipe is connected between one side of each of the outer swivel fittings and the respective conduit, and each inner pipe connects the other side of each of the outer swivel fittings to a respective side of the inner swivel fitting. The two conduits being interconnected are normally connected at locations where they run parallel to each other and wherein all of their relative motion is in the plane they define. The swivels are effective about swivel axes substantially perpendicular to this plane, with the inner pipes inclined to the plane and the outer pipes perpendicular thereto. Such an arrangement allows considerable shifting of the pipes relative to each other, both toward and away from each other and longitudinally relative to each other.
Each such fitting, although it allows swivelling of its sides relative to each other, nonetheless transmits at least a limited amount of torsion between its sides. Thus any relative shifting of the two conduits being interconnected will be transmitted at least in part as a strain to the joints at each end of each of the outer pipes. This strain is particularly harmful at the joint where each of the outer pipes connects to the respective conduit. Such a joint is typically welded, and is usually the failure point of such a connecting system.
Normally each of the outer pipes is provided with a cut off valve. Failure at the joints between each of the outer pipes and the respective conduit has the enormous disadvantage that it is necessary to shut down the entire system for repair. Any failure between the cut-off valves in the outer pipes, that is in the inner ends of the outer pipes, in the swivel fittings, or in the inner pipes, can normally be taken care of without shutting down the whole system merely by cutting off this part of the flow path with the two cut off valves.